sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Hardness: 6
Color: Brown, tan, gray
Luster: Dull to waxy

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brown, tan, gray; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8

Formation & geological history

Formed by the accumulation of siliceous remains (diatoms or radiolaria) in deep-sea environments or through the precipitation of silica in groundwater within limestone or chalk beds. Most specimens can date back hundreds of millions of years.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate, road base, and as a decorative stone in landscaping.

Geological facts

Chert is so hard it can scratch steel and was the primary material for arrowheads and spears used by early humans due to its ability to produce sharp edges when fractured.

Field identification & locations

Identify by its waxy luster, hardness, and conchoidal (shell-like) fracture patterns. It is extremely common in areas with limestone bedrock or along riverbeds where the harder chert resists weathering.